1. Field of the Invention
The present invention relates to an engine having a variable compression ratio, and to methods of operating the engine. More particularly, the present invention relates to an engine in which the effective length of a connecting rod is made hydraulically adjustable to allow for adjustment of the compression ratio, and to methods of operating the described engine.
2. Background Art
Conventionally, it has been known that some vehicles such as cars may use a variable compression ratio engine, that provides an appropriate compression ratio according to driving conditions, by making an intermediate portion of a connecting rod flexibly adjustable. A flexing portion of the connecting rod needs to be movable while the engine is operating. Doing so requires a driving force of an actuator that exceeds the engine's inertia force, or an air-fuel mixture's explosion force acting on the flexing portion. Improving the control accuracy requires a large external energy or a complicated mechanism (see, e.g., Japanese published patent document JP-A 214770/2001).
By contrast, another technology is described in Japanese published patent document JP-A 289079/2001. This technology uses the engine's inertia force and the air-fuel mixture's explosion force acting on an operating piston as a differently directed force alternately acting on the flexing portion of the connecting rod. This force is used to operate a control mechanism connected to the connecting rod's flexing portion via a control rod. The control mechanism comprises two arced spaces that are separated by a moving vane, and are filled with hydraulic fluid. The hydraulic fluid is selectively ported from one space to the other, via a check valve, against the above-mentioned differently directed force This makes it possible to change or retain a flexing orientation of the connecting rod.
The technology described in Japanese published patent document JP-A 289079/2001 effectively uses the engine's inertia force and the air-fuel mixture's explosion force acting on the piston. There is an advantage of not requiring an extra power. However, the control mechanism is structured to be the two arced spaces that are separated by the moving vane. There are problems of complicating the structure and difficultly of ensuring sealability of the mechanism.
Although the known variable compression ratio engines are useful, a need still esists for an improved variable compression ratio engine that has a simple structure, ensures sealability, and provides high reliability.